Peripheral grinding wheel



Aug. 4,' 1970 H. c. MILLER PERIPHERAL GRINDING WHEEL 3 Sheets-Sheet 1Filed Dec. 13, 1967 FIG. 2

INVENTOR:

HAROLD C. M I LL ER Aug. 4, 1970 H; c. MILLER 3,522,576

PERIPHERAL GRINDING WHEEL I Filed Dec. 1:5, 1967 3 Sheets-Sheet 2INVENTORI HAROLD C. MILLER g- 1970 H. c. MILLER 3,522,676

PERIPHERAL GRINDING WHEEL Filed Dec. 13, 1967 3 Sheets-Sheet 3 INVENTORI HAROLD (3. MI LLER By 7/ M 3,522,676 PERIPHERAL GRINDING WHEEL HaroldC. Miller, Chicago, Ill., assignor to Super-Cut, Inc., Chicago, 11]., acorporation of Illinois Filed Dec. 13, 1967, Ser. No. 690,201 Int. Cl.B24d 7/02 US. Cl. 51-206 4 Claims ABSTRACT OF THE DISCLOSURE Aperipheral abrasive grinding wheel in which the annular grinding memberis formed from powdered materials by the application of radial pressurein the presence of heat. Radial pressure is applied to the grindingmember by establishing an annular mold cavity, the inner wall of whichis in the form of a backing ring, which, when heated, becomessufficiently ductile that it may be stretched to enlarge its radialdimension, thus compressing the materials in the cavity radially, andalso bonding such inner wall to the compressed grinding member so thatit becomes a permanent backing ring therefor when the other mold wallsare removed.

The present invention relates to an abrasive grinding wheel of the typewhich is commonly referred to as a peripheral grinding wheel. Such awheel ordiniarly comprises a flat circular steel body or hub, theperiphery of which is surrounded by an annular grinding member in theform of a sintered metal or other matrix having uniformly distributedtherethrough crushed or fragmented diamonds or other hard abrasiveparticles such as tungsten carbide, silicon carbide or fused alumina.

Heretofore, and as exemplified in US. Patent No. 3,369,879, granted onFeb. 20, 1968 and entitled Method of Making a Peripheral DiamondGrinding Wheel, it has been the practice to fabricate a peripheralgrinding wheel by establishing an annular mold cavity around theperiphery of a circular metallic hub, the cavity being defined by theperiphery of the hub itself together with an outer encompassing moldring and two opposed laterally movable mold rings. A mold mixtureconsisting of powdered metal or other fusible powder with uniformlydistributed abrasive particles therein is placed in the mold cavity andthe relatively movable mold rings are forced towards one another duringthe application of heat to the mold cavity in order to sinter or fusethe powdered metal or other material and reduce the width of the moldcavity to the desired dimension which usually is the width or thicknessof the metal hub. After cooling, the three mold rings are removed andthe thus formed annular grinding member remains bonded to the peripheryof the hub and these two bonded-together parts constitute the finishedgrinding wheel.

Such a method has proven quite satisfactory in connection with theformation or fabrication of narrow grinding wheels where the lateralwidth of the annular grinding members does not exceed one and one-halfinches. However, it has been found in connection with the fabrication ofWider grinding wheels such, for example, as wheels having annulargrinding members of a width on the order of two inches or more, thatthis method is not altogether satisfactory. Where grinding wheels havingannular grinding members as wide as four inches are concerned, theaforementioned method is entirely without value. The reason for this isthat the tremendous pressure that is required for proper sintering orfusing must be equally distributed throughout the filled mold cavity inorder to avoid soft spots of low density in the finished annulargrinding member. Where an axially long, but radially narrow, mold iscon-- cerned, the frictional opposition that is offered to the flow ofthe powdered metal or other fusible material in the mold cavity bymovement of the laterally movable mold rings towards one another doesnot enable full molding pressure to reach the central regions of themold cavity with the result that proper and complete sintering or fusingof the powdered matrix material takes place only near the end regions ofsaid mold cavity. In other words, Pascals principle of pressuretransmission within a confined fluid does not apply.

The present invention makes possible the satisfactory fusing of apowdered matrix-producing material in situ on the periphery of a steelor other metal grinding wheel hub to a width far in excess of theaforementioned tolerable width. Commercial peripheral diamond grindingwheels having annular grinding members on the order of four inchesalready have been made according to the present invention and there isno reason to suppose that there is any limit to the width which may beaccommodated by such method.

According to the present invention, instead of applying lateral or axialinward pressure to the mold mixture within the mold cavity, radialoutward pressure is applied to the mixture. Thus, since the annular moldcavity is of extremely small radial thickness, relatively speaking,uniform compacting of all portions of the mold mixture in the moldcavity along its width will take place and thus the particular width ofthe mold cavity and consequently of the annular grinding member to beformed) is of no consideration. The mechanical difficulties which areposed in applying radial outward pressure to the mold mixture in theannular mold cavity have been overcome by utilizing a rigid outer moldwall or ring, a pair of opposed rigid mold walls, and a radiallyexpansible inner mold wall, the latter constituting all, or a portionof, the wheel hub and the four walls defining a radially shrinkable orcompressible mold cavity. Means are provided for effecting uniformoutward radial expansion of the inner mold wall in the presence of heat,thus resulting in magnified circumferential expansion thereof, advantagebeing taken of the stretchability of the metal of the inner mold wall topermit such expansion. To effect such radial and circumferentialexpansion, a pair of opposed cam rings having frusto-conical camsurfaces are forced into the side regions or confines of the inner moldwall so as to exert the necessary spreading action incident to radialexpansion of said inner mold wall. The heated environment in which thisspreading action takes place supplies the necessary heat for fusing thepowdered component of the mold mixture, as well as for rendering theinner mold wall so sufficiently ductile that it will succumb to theradial expansion and remain in its expanded state after cooling. Theperipheral grinding wheel resulting from such a method of applyingradial pressure to a mold mixture (admixture of powdered metal or othermaterial and abrasive particles) which is confined in the vicinity ofthe periphery of a grinding wheel hub, or of a portion of such a hub,constitutes the principal object of the present invention.

In practicing the aforementioned method commercially, and in themanufacture of various forms of peripheral diamond grinding wheels, ifit is desired that a finished peripheral diamond grinding wheel shallemerge from the molding operation, the aforementioned cam rings,together with the inner mold wall, are caused to constitute a compositethree-part grinding wheel hub, the assembly of which produces thenecessary radial expansion of the inner mold wall. If it is desired thatthe user of the wheel shall supply his own hub assembly, then atemporary composite hub, likewise comprised of two cam rings and aninner mold wall, is employed but the two cam rings are made removable sothat after the temporary hub has been created during the moldingoperation, the cam rings may be removed, leaving only the inner moldwall to which the annular grinding member is firmly bonded by reason ofthe molding operation. In these two respects, two basic modifications ofthe present method are contemplated and the practicing thereof will bedescribed in detail presently. Further modifications of a minor naturehave been developed, one such modification affording a convenient meansfor exposing the interior of the mold cavity for filling purposes priorto resorting to the step of causing radial expansion of the inner moldwall, this latter modification also being described in detailsubsequently.

Insofar as the employed apparatus for practicing the above-outlinedmethod is concerned, the use of cooperating frusto-conical cam surfacesof small slant angle to effect radial expansion of the inner mold wallin a heated environment produces a powerful outward radial thrust on theinner expansible mold wall far in excess of that attained by such knownmeans for expanding a ring radially as the utilization of hydraulicexpanding devices or sliding split ring arrangements in combination withtoggle members.

In connection with the completed peripheral grinding wheel, whether theannular grinding member be applied to a complete hub or merely to anouter hub ring as previously described, the structure evolved frompracticing the present method, particularly where a wide annulargrinding member is concerned, is of a superior nature in that it isdevoid of areas of low density while at the same time a firm bondbetween the annual grinding member and its supporting ring (i.e., theinner mold wall) is obtained coextensively along the entire annularinterace.

In the accompanying three sheets of drawings forming a part of thisspecification, several illustrative embodiments of the peripheralgrinding Wheel constituting the present invention are shown.

In these drawings:

FIG. 1 is a perspective view of a peripheral diamond grinding wheelembodying the invention and constructed according to the aforesaidmethod, the wheel having a confined annular grinding member (sintered orfused metal or other matrix with crushed or fragmented diamond particlesdistributed uniformly throughout);

FIG. 2 is an enlarged radial sectional view taken on the line 2-2 ofFIG. 1;

FIG. 3 is a sectional view similar to FIG. 2 but showing a modified formof grinding wheel in which the side portions thereof have been milledaway to expose the sides of the annular grinding member;

FIG. 4 is a perspective view of a backing ring and annular grindingmember assembly, the assembly being designed for removable mounting on aseparately fabricated hub assembly;

FIG. 5 is an enlarged radial sectional view taken on the line 55 of FIG.4;

FIG. 6 is a sectional view similar to FIG. 5 but showing a slightlymodified form of backing ring and annular grinding member assembly;

FIG. 6a is a fragmentary radial sectional view taken through an outermold ring which is employed in forming the backing ring and annulargrinding member assembly of FIG. 6;

FIG. 7 is a sectional view similar to FIGS. 5 and 6 but showing afurther modified form of back ring and annular grinding member assembly;

FIG. 7a is a fragmentary radial sectional view taken through an outermold ring which is employed in forming the backing ring and annulargrinding member assembly of FIG. 7;

FIG. 8 is a perspective view of a fragment of the inner mold ring whichis employed in fabricating the peripheral diamond grinding wheel of FIG.1;

FIG. 9 is a fragmentary sectional view taken substantially centrally andvertically through the various mold parts which are employed inconnection with the method of the present invention, such view showingthe parts in the relative positions which they assume immediately priorto the fusing and molding operation in the production of the grindingwheel of FIG. 1;

FIG. 10 is a sectional view similar to FIG. 9 but showing the mold partsin the positions which they assume during the fusing and moldingoperation; and

FIGS. 11 and 12 are sectional views similar to FIGS. 9 and 10,respectively, showing the production of the backing ring and annulargrinding member assembly of FIG. 4.

Referring now to the drawings in detail and in particular to FIGS. 1 and2, there is illustrated in detail a peripheral grinding wheel which isformed by the method hereinafter described, the Wheel being designatedin its entirety by the reference numeral 10. The wheel is of a compositenature and consists of (1) an inseparable twopart metal hub 12 whichpreferably is formed of steel, (2) an annular grinding member 14, and(3) a backing ring 16 for the annular grinding member, the backing ringlikewise preferably being formed of steel. The structuralcharacteristics of the grinding wheel 10 are largely a result of themethod by means of which the wheel is formed, which is not to say thatthe structural features thereof do not, in themselves, vary widely froma conventional grinding wheel which is designed for the same purpose.However, since a full description of the method will be set forthsubsequently, the present description of the grinding wheel 10 will belimited almost entirely to its structural make-up, reference to themethod being made only in the interests of clarifying the grinding wheelstructure and paving the way for a better understanding of the methodwhen its description is undertaken subsequently.

Still referring to FIGS. 1 and 2, the annular grinding member 14 is inthe form of a continuous, ring-shaped, matrix (fused metal or otherpowder) with diamond or other abrasive particles distributedsubstantially uniformly throughout the same. The member 14 encompassesthe metal backing ring 16 and its inner periphery or side is bonded tothe outer periphery or side of the backing ring by reason of eithersoldering or the compacting and fusing operation which is performed onthe originally loose metal or other powder and abrasive particles in thepresence of heat and which results in fusing of the opposed peripheralsurfaces or sides of the two parts, all in a manner that will bedescribed in greater detail when the nature of the present method is setforth. The bond between the annular grinding member 14 and the backingring 16 is enhanced by the provision of a multiplicity of concentric,circular or circumferential striations 18 (see FIG. 8) which areprovided on the outer and otherwise cylindrical side 20 of the backingring. The backing ring 16 has substantially the radial crosssectionalshape of an isosceles triangle of small slant angle and this ringencompasses the main body portion of the composite hub 12 and seatssquarely within a peripheral recess which is of V-shaped cross sectionand is provided in the periphery of the hub. The recess is formed byreason of the bringing together of the two sections 22 and 24 of thetwo-part hub 12, the sections being provided respectively withfrusto-conical surfaces 26 and 28 which are of small slant angle andsmall slant height and come together in diabolo or hourglass fashionwhen the inner side faces of the section are brought together inface-to-face contact or abutment along a common meeting plane orinterface 30. Except for the provision of a small centrally locatedannular flat 32 on the inner side of the annular grinding member 16,this inner side is shaped conformably to the V-shaped contour of theaforesaid recess and embodies adjacent and oppositely extendingfrusto-conical surfaces 26a and 28a corresponding and shaped similarlyto the frusto-conical surfaces 26 and 28 of the hub sections 22 and 24.Small annular grooves 34 are formed in and extend around thefrustoconical surfaces 26 and 28 and are provided for reception oflengths of brazing wire or solder prior to subjecting the parts to theapplication of heat in performing the brazing or soldering operation. Alayer or coating of brazing or soldering compound also unites and/orbonds together the two sections 22 and 24 of the two-part metal hub 12.Outwardly and radially extending retaining flanges 36 straddle theannular grinding member 14 and these flanges are integral parts of thehub sections 22 and 24 and come within the sphere of influence of themolten brazing or soldering material during the heating operation sothat they are thus bonded to the sides of said annular grinding member.The hub 12 may be provided with any desired mounting facilities by meansof which it may be secured to a rotatable power shaft. Accordingly, acentral arbor-receiving hole 38 is provided through the hub, this holeresulting from the provision of mating central holes 40 and 42 in thetwo hub sections 22 and 24.

Referring now to FIGS. 9 and wherein there is illustrated the method bymeans of which the grinding wheel 10 is constructed, the assembly of thevarious grinding wheel parts described above is made by utilizing thetwo hub sections, as well as the backing ring 16 as relatively movablemold parts, an additional mold part in the form of an outer mold ring 50being employed. The assembly is preferably made in a mold pressincluding a lower press platen 52 and an upper press ram 54. Theassembly is made by placing either hub section, as, for example, thesection 22, on the platen 52 in a horizontal position and then causingthe outer portion of the inner frusto-conical surface 26a of the backingring 16 to rest on the inner portion of the frusto-conical surface 26 ofthe hub section 22 (see FIG. 9) so that the backing ring projectsupwardly above the level of the section 22 an appreciable distance. Aquantity of brazing material is spread on the upper side surface 54 ofthe hub section 22 and a length of wire-type silver solder or the likeis disposed in the annular groove 34 in the frustoconical surface 26 ofthe thus positioned hub section 22. The other hub section 24 is thenplaced or superimposed in a similar manner on the backing ring 16 and sopositioned that the inner portion of the frusto-conical surface 28 seatson the outer portion of the frusto-conical surface 28a of the backingring 16, a length of silver solder being first placed in the groove 34in said frusto-conical surface 28 of said other hub section 24.Thereafter, the outer mold ring 50 is telescopically received over thetwo hub sections 22 and 24. The minimum internal diameter of the backingring 16 is less than the minimum diameter of either hub section and themaximum external diameter of both frusto-conical surfaces 26 or 28 isgreater than the maximum internal diameter of both inner frustoconicalsurfaces 26a and 28a of the backing ring 16. Additionally, the slantheight of all four of the frustoconical surfaces is equal, with theslant angle thereof being on the order of 40 or less. The net result ofsuch proportioning or dimensioning of the parts (hub sections 22 and 24and backing ring 16) is such as to establish a continuous annular moldcavity 60 when the various mold parts are assembled loosely as describedabove and as shown in FIG. 9. This mold cavity 60 is a variable volumecavity and it is defined by the inside cylindrical surface of the outermold ring 50, the striated outer surface of the backing ring 16, alimited portion of each frusto-conical surface 26 and 28, and the twoopposed inner surfaces of the retaining flanges 36. In making orfabricating the wheel 10 by way of the mold, it is contemplated that themold cavity will be suitably filled with the mold mixture before theparts of the mold structure or apparatus are fully assembled.

From the above description, it will be apparent that by causing the twohub sections 22 and 24 to move relatively toward each other in responseto downward movement of the upper press ram 54, a powerful cammingaction will be exerted upon the backing ring 16 tending to stretch thelatter in a radial direction, thus causing the same to increase itsdiameter and exert a radial compressional force on the mold mixture(fusible powdered metal or other material with abrasive particlesdistributed uniformly throughout) which is introduced into the moldcavity 60. At the same time, the two opposing surfaces of the shoulders36 move toward each other and offer a limited amount of transversecompressional force to the mold mixture within the cavity. The moldmixture is thus compressed in all directions, but the compressionthereof is largely radial. When the two hub sections 22 and 24 are movedtoward each other in the presence of heat, the molecular tenacity of themetal backing ring is reduced to such an extent that it will readilyyield to the radial forces tending to stretch it. The necessary heat maybe supplied to the assembled parts in the vicinity of the backing ring16 in any suitable manner as, for example, by application to the moldring of a series of inwardly directed flame jets 62 issuing from agaseous fuel burner ring 64.

The final position of the various mold parts is shown in FIG. 10 whereinit will be noted that the upper hub section 24, having moved downwardlyand into face-to-face contact with the lower hub section 22, has becomebonded to this latter section coextensively along the interface 30 whileat the same time the converging inner frusto-conical surfaces 26a and28a of the metal backing ring 16 have become bonded to thefrusto-conical surfaces 26 and 28 of the two hub sections, such bondingtaking place by reason of the capillary flow of solder over thesesurfaces in the presence of flux. The camming engagement between thefrusto-conical surfaces 26 and 28 of the hub sections 22 and 24 and thefrusto-conical surfaces 26a and 28d of the backing ring 16 causes thering to stretch outwards and thus increase its radial dimension so as tocompress the mold mixture in a radial direction against the outerreaction mold ring 50, while at the same time limited transversecompression of the mixture between the retaining flanges 36 is caused totake place. Due to fusing of the powdered metal or other material in themold cavity 60 under the influence of heat and pressure, the compactedannular grinding member 14 becomes bonded to the outer striated side 20of the backing ring 16.

It is to be noted at this point that during descent of the upper pressram 54 sliding of the frusto-conical surfaces 26 and 28 of the hubsections 22 and 24 on the inner frusto-conical surfaces 26a and 28a ofthe backing ring 16 brings the sharp circular lateral edges of thebacking ring against the annular retaining flanges 36 while the opposedmeeting inner side surfaces of the two hub sections 22 and 24 cometogether and establish a small void in the vicinity of the annular flat32 on the backing ring 16. This flat 32 is provided in order toaccommodate any discrepancy in manufacturing tolerances which mightotherwise prevent square seating of the two hub sections 22 and 24 oneach other.

A series of channels 62 are formed in both the lower press platen 52 andthe upper press ram 54 for circulation of a coolant fluid therethroughto prevent undue heat accumulation in these parts during formation ofthe grinding member.

In FIG. 3, a slightly modified form of grinding wheel is shown, thiswheel being constructed and assembled by the same method that isillustrated in FIGS. 9 and 10, and in the same mold apparatus. The onlydifference between the wheel 110 and the wheel 10 is that the outer sideportions of the hub sections 122 and 124 have been milled away to suchdepth that there are no outwardly extending annular retaining flanges36, thus exposing the side surfaces of the annular grinding member 114.In order to avoid needless repetition of description, similar referencenumerals but of a higher order are applied to the corresponding parts asbetween the disclosures of FIGS. 3 and 2. The grinding wheel 10 with itsannular retaining flanges 36 may be found useful in shaping the edges ofa sheet of glass, whereas the grinding wheel 110 which is devoid of suchflanges may be caused to operate upon a flat planar surface.

Whereas in the manufacture of either the grinding wheel 10 of FIGS. 1and 2 or the grinding wheel 110 of FIG. 3, the two hub sections as wellas the backing ring constitute movable cavity-forming mold parts whichremain bonded to one another and are allowed to remain bonded so as tobecome actual elements of the finished Wheel, it may be desirable incertain instances to supply only a reinforced or backed peripheralgrinding wheel subassembly as a salable article to which the purchasermay afiix his own hub structure. Such a reinforced subassembly isillustrated in FIGS. 4 and 5 and is designated in its entirety by thereference numeral 210. Again, in order to avoid repetition ofdescription, similar reference numerals of a still higher order areemployed in order to designate the corresponding parts as between thedisclosures of FIGS. 5 and 3. To produce the two-piece peripheralgrinding wheel subassembly 210 including only an annular grinding member214 and its backing ring 216, the mold structure or apparatus of FIGS.11 and 12 is employed. Utilizing corresponding reference numerals of ahigher order as between the disclosures of FIGS. 11 and 12 and FIGS. 9and 10, the mold apparatus of FIGS. 11 and 12. remains substantially thesame as the mold apparatus of FIGS. 9 and 10 except for the fact thatthe upper mold ring 224 is formed of two parts 225 and 227, the annularsolder-retaining grooves 34 are omitted, and the upper and lower moldrings, as well as the outer mold ring 250 are preferably, but notnecessarily, formed of graphite. By omitting the application of solderto the interface between the upper and lower mold rings 224 and 222,removal of these rings after the sintering operatiOn has been completedis made possible since there is no tendency for these parts to adhere toeach other or to the steel backing ring 216. Removal of the outer moldring 250 also is facilitated.

The upper mold ring 224 is made of the two parts 225 and 227 in order tofacilitate filling of the mold cavity 260 with the mold mixture. Adepending annular flange 229 on the inner marginal portion of the upperpart 227 of the upper mold ring 224 establishes an interlock between theparts 225 and 227 for centering purposes. It will be observed thatbefore the upper part 227 is applied during mold assembly operations,the upper rim of the annular mold cavity 260 is exposed for fillingpurposes. After the cavity has been filled with the proper amount ofloose mold mixture, the part 227 may be placed on the part 225 to closethe filling opening, after which the molding process may take place inthe same manner as described in detail in connection with the moldstructure or apparatus of FIGS. 9 and 10.

In FIG. 6, a further modified form of reinforced peripheral grindingWheel subassembly is disclosed and it is designated in its entirety bythe reference numeral 310. The annular grinding member 312 is ofconcave-convex radial cross section with its convex side facingoutwardly, and the backing ring 316 is formed with an outer convexstriated outer side 320 to accommodate the convex inner surface of theannular grinding member. Similarly, in the molding process or methodwhich is conducted in accordance with the principles set forth inconnection with FIGS. 11 and 12, the outer mold ring 350 (see FIG. 6a)is formed with a concave inner surface 351 in order to accommodate theconvex outer surface of the annular grinding member. The actual moldingand milling procedures which are employed in connection with the manufacture of the reinforced peripheral wheel subassembly 310 of FIG. 6 donot deviate from those that are employed in the manufacture of thereinforced grinding wheel subassambly 210.

In FIG. 7 yet another form of reinforced peripheral grinding wheelsubassembly is shown and it is designated by the reference numeral 410.The annular grinding member 414 is of concavo-convex radial crosssection with its concave side facing outwardly. The outer mold ring 450(see FIG. 7a) which is employed in connection with the molding apparatusfor forming the subassembly 410 has an inner convex surface 451 and itis conformable to the outer exposed concave surface of the annulargrinding member 414.

Having thus described the invention what I claim as new and desire tosecure by letters patent is:

1. As a new article of manufacture, in combination, a composite grindingannulus including a continuous annular grinding member comprised of amatrix having abrasive particles disposed therein and presenting inner,outer and side surfaces, and a metal backing ring disposed within saidgrinding member in concentric relationship and having an outer surfacebonded coextensively to the inner surface of the grinding member, saidbacking ring having a uniform cross-sectional area which generally is inthe form of a relatively flat isosceles triangle of small slant angleand small slant height with the apex thereof facing inwardly and withthe sides thereof merging with the base in the respective planes of theside surfaces of the grinding member.

2. As a new article of manufacture, the combination set forth in claim 1and including, additionally, a series of circumferential striationsextending completely around the outer surface of the backing ring toenhance the bond between said surface and the matrix.

3. As a new article of manufacture, the combination set forth in claim 1and including, additionally, a composite hub for said grinding annulusand comprising two frusto-conical hub sections having sides disposed inintimate coextensive contact with the sides of the backing ring andhaving their small bases in coextensive contact with each other andbonded together.

4. As a new article of manufacture, the combination set forth in claim 3and wherein the sides of the hub sections are bonded to the sides of thebacking ring.

References Cited UNITED STATES PATENTS 1,695,647 12/1928 Furler 29-782,950,582 8/ 1960 Beauchaine 5l206 X 3,116,536 1/1964 Tobey 29-78 OTHELLM. SIMPSON, Primary Examiner U.S. Cl. X.R. l8l6.5; 51-309

